Process of treating a lignocellulosic material

ABSTRACT

A process of treating a lignocellulosic material includes a pre-extraction step in which hemicellulose is extracted from the lignocellulosic material. In one embodiment, the pre-extraction step involves contacting the lignocellulosic material with an aqueous solution under conditions that release acidic material from the lignocellulosic material into the aqueous solution, and the aqueous solution includes a basic material that at least partly neutralizes the acidic material so that the aqueous solution at the end of the pre-extraction step has a pH within a range of from 4.5 to 11. The process also includes a pulping step, after the pre-extraction step, in which the lignocellulosic material is separated into pulp. The process further includes an adsorption step, after the pulping step, in which hemicellulose is adsorbed on the pulp.

BACKGROUND OF THE INVENTION

This invention relates in general to processes of treatinglignocellulosic materials and in particular to a process of producing alignocellulosic pulp such as a wood pulp.

Lignocellulosic materials, such as wood, are plant materials made upprimarily of cellulose, hemicellulose and lignin. The cellulose is thechief structural element and major constituent of the plants. Itconsists of a fibrous cellulose portion made from polymeric chains thatare aligned with one another and form strong associated bonds withadjacent chains. The lignin is a three-dimensional polymeric materialthat bonds the cellulosic fibers and is also distributed within thefibers themselves. Lignin is largely responsible for the strength andrigidity of the plants. The hemicellulose is a polysaccharide that is acomponent of the cell walls of the plants. The two major classes ofhemicellulose are glucomannans and xylans.

The wood is converted to pulp for use in paper manufacturing. Pulpcomprises wood fibers capable of being slurried or suspended and thendeposited on a screen to form a sheet of paper. There are two main typesof pulping techniques: mechanical pulping and chemical pulping. Inmechanical pulping, the wood is physically separated into individualfibers. In chemical pulping, the wood chips are digested with chemicalsolutions to solubilize portions of the lignin and hemicellulose andthus permit their removal in the waste pulping liquor. The commonly usedchemical pulping processes include the kraft process, the sulfiteprocess, and the soda process. The kraft process is the most commonlyused and involves digesting the wood chips in an aqueous solution ofsodium hydroxide and sodium sulfide. The wood pulp produced in thepulping process is usually separated into a fibrous mass and washed.

The wood pulp after the pulping process is dark colored because itcontains residual lignin not removed during digestion which has beenchemically modified in pulping to form chromophoric groups. In order tolighten the color of the pulp, so as to make it suitable for white papermanufacture, it is necessary to remove the residual lignin by use ofdelignifying materials and by chemically converting any residual lignininto colorless compounds by bleaching. Delignification and bleaching ofwood pulp have been carried out with materials such as chlorine, oxygenor ozone.

U.S. Pat. No. 4,436,586 by Elmore discloses a method for producing bothkraft pulp and alcohol from hardwood chips or the like. The chips aresubjected to mild acid prehydrolysis following by mild causticpre-extraction. The withdrawn hydrolysate has insufficient furfural toinhibit microorganism growth, and both the hexose and pentose sugars inthe hydrolysate are fermented to ultimately produce ethanol, butanol, orthe like. The chips, after caustic pre-extraction, are subjected to asulphate cook, and a wash, and the resultant pulp is a kraft pulp saidto have viscosity and tear strength characteristics more desirable thanconventional kraft pulp. The pulp can be subjected to oxygendelignification, and it can achieve a higher K number in fewersubsequent bleaching stages than conventional kraft pulp.

SUMMARY OF THE INVENTION

This invention relates to a process of treating a lignocellulosicmaterial. The process includes a pre-extraction step in whichhemicellulose is extracted from the lignocellulosic material. In oneembodiment, the pre-extraction step comprises contacting thelignocellulosic material with an aqueous solution under conditions thatrelease acidic material from the lignocellulosic material into theaqueous solution, and the aqueous solution includes a basic materialthat at least partly neutralizes the acidic material so that the aqueoussolution at the end of the pre-extraction step has a pH within a rangeof from about 4.5 to about 11. The process also includes a pulping step,after the pre-extraction step, in which the lignocellulosic material isseparated into pulp. The process further includes an adsorption step,after the pulping step, in which hemicellulose is adsorbed on the pulp.

In another embodiment, the process includes a pre-extraction step inwhich hemicellulose is extracted from the lignocellulosic material bycontacting the lignocellulosic material with an aqueous solution underconditions that release acidic material from the lignocellulosicmaterial into the aqueous solution, and the aqueous solution includes abasic material that at least partly neutralizes the acidic material sothat the aqueous solution at the end of the pre-extraction step has a pHwithin a range of from about 4.5 to about 11. The process also includesa pulping step, after the pre-extraction step, in which thelignocellulosic material is separated into pulp. Further, the processexcludes the use of an acid hydrolysis step before the pulping step.

In another embodiment, the process comprises providing a pulp from alignocellulosic material, and adsorbing hemicellulose on the pulp toincrease the yield of the pulp.

In a further embodiment, the process comprises providing a pulp from alignocellulosic material, then adsorbing hemicellulose on the pulp, andthen subjecting the pulp to a delignification process to remove ligninfrom the pulp. The adsorbed hemicellulose increases the selectivity ofthe delignification process compared to the same process without theadsorbed hemicellulose.

Various advantages of this invention will become apparent to thoseskilled in the art from the following detailed description of thepreferred embodiments, when read in light of the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a process of treating a wood chips toproduce pulp, the process including pre-extraction and adsorption steps.

FIGS. 2-11 are graphs displaying the result of processes described inExample 6. In particular, FIG. 2 shows that the total pulp yield versuskappa number relationship for pre-extraction/kraft cooks runs parallelto that of the kraft control cooks over a range of bleachable pulp kappanumbers.

FIG. 3 shows the effect of effective alkali (EA) charge during a kraftcook on the total pulp yield for Na₂CO₃ pre-extraction/kraft cooks ascompared to that of a control kraft cook at 15% EA charge.

FIG. 4 shows that at the same kappa number the total pulp yield afterpre-extraction with 4% NaBO₂ followed by kraft cooking at 12% EA chargeis about 0 to 0.5% lower than that of the control kraft cook at 15% EAcharge.

FIG. 5 shows that at the same kappa number the total pulp yield afterextraction with Na₂CO₃ plus 0.05% AQ followed by kraft cooking at 12% EAcharge is almost 1% higher than that of the control kraft cook at 15% EAcharge.

FIG. 6 shows that the delignification rate for the Na₂CO₃pre-extraction/kraft cooks is higher than that of the control kraftcook, while that of the NaBO₂ pre-extraction/kraft cook is lower thanthat of the control kraft cook.

FIG. 7 shows the effect of the EA charge during the kraft cook of theNa₂CO₃ pre-extraction/kraft cooks.

FIG. 8 shows the slower delignification rate of the NaBO₂pre-extraction/kraft cook relative to the control kraft cook.

FIG. 9 shows the effect of these delignification rates on thedevelopment of the kappa number versus the H-factor.

FIG. 10 shows that the Na₂CO₃ extraction/kraft cooks at 13% EA chargeproduce a black liquor of about 0.5% higher residual effective alkali(REA) than that of the kraft control cooks with 15% EA charge at thesame final kappa number, while there is little difference in REA betweenthe control kraft cook and the Na₂CO₃ extraction/kraft cook at 12% EA.

FIG. 11 shows the percentage of screen rejects versus kappa number forthe Na₂CO₃ and NaBO₂ pre-extraction/kraft cooks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The lignocellulosic material which is treated in the process of theinvention can be any plant material made up primarily of cellulose,hemicellulose and lignin. In some embodiments the lignocellulosicmaterial is wood, such as hardwood or softwood. The lignocellulosicmaterial can be in any suitable form at the start of the process. Insome embodiments the lignocellulosic material is in a comminuted form,for example in the form of wood chips. FIG. 1 is a block diagram of aprocess according to one embodiment of the invention. It is seen thatthe process starts with wood chips.

In the embodiment shown in FIG. 1, the wood chips are subjected to apre-extraction step of the process. Conventional wood pulping processesdo not include such a pre-extraction step. In the pre-extraction step,hemicellulose is extracted from the wood chips. In some embodiments, thepre-extraction step achieves the extraction of at least about 4%, atleast about 10%, or at least about 15% of the hemicellulose from thelignocellulosic material as measured on a dry material weight basis (anoven dry wood weight basis in the illustrated embodiment).

The hemicellulose extraction can be accomplished in any suitable manner.In one embodiment, the hemicellulose is extracted by contacting thelignocellulosic material with an aqueous solution that includes a basicmaterial such as an alkali material. Any suitable basic material can beused in the pre-extraction step. Some nonlimiting examples includealkali metal hydroxides, alkali metal borates, alkali metal carbonates,and mixtures thereof.

Optionally, the aqueous solution can also include an additive thatbenefits the process by one or both of the following: improvingextraction of the hemicellulose from the lignocellulosic material duringthe pre-extraction step, or improving separation of the lignocellulosicmaterial into pulp during the pulping step (described below). Anysuitable additive can be used, for example, an additive selected fromanthraquinones, anthraquinone derivatives, or mixtures thereof.

The pre-extraction step can be conducted using any suitable processequipment and conditions. In one embodiment, the lignocellulosicmaterial is soaked in the aqueous solution such that it becomesimpregnated with the solution, and the temperature of the solution israised and held at an elevated temperature for a suitable time to reachthe desired pH. In some embodiments the conditions of the pre-extractionstep include a temperature of extraction as for example within a rangeof from about 110° C. to about 180° C.,e.g. from 130° C. to about 170°C., or from about 135° C. to about 165° C., and a time of extractionwithin a range of from about 30 minutes to about 150 minutes, e.g., fromabout 45 minutes to about 120 minutes.

Contacting the lignocellulosic material with the aqueous solution duringthe pre-extraction step may cause acidic material(s) to be released fromthe lignocellulosic material into the solution. For example, such acidicmaterials may include wood sugars and to a lesser extent lignin. Thewood sugars include the extracted hemicellulose and other sugars. In oneembodiment, the aqueous solution at the beginning of the pre-extractionstep is sufficiently basic to at least partly neutralize the acidicmaterial(s) released during the extraction, so that the aqueous solutionat the end of the pre-extraction step has a pH within a range of fromabout 4.5 to about 11.0, e.g. from about 5 to about 10 or from about 5to about 9.5, when measured at a temperature of 20° C. In a particularembodiment, the aqueous solution at the end of the pre-extraction stepis a near-neutral solution having a pH within a range of from about 6 toabout 8.

The process may further include a solution removal step, following thepre-extraction step, in which at least part of the aqueous solutionincluding extracted hemicellulose is removed from the lignocellulosicmaterial. In one embodiment at least about 60 wt %, e.g., at least about75 wt %, of the aqueous solution is removed from the lignocellulosicmaterial. The solution can be removed/withdrawn in any suitable manner.

In one embodiment, at least part of the aqueous solution removed fromthe lignocellulosic material is recycled by adding it to the aqueoussolution at the beginning of the pre-extraction step. The process shownin FIG. 1 includes recycling of part of the removed aqueous solution.The recycling reduces the water concentration and increases thedissolved solids (e.g., sugar) concentration in the aqueous solution.

The process of the invention includes a pulping step in someembodiments. The pulping step follows the pre-extraction step andsolution removal. In the pulping step, the lignocellulosic material isseparated into pulp, e.g., into wood pulp when wood is used as thestarting material. Any suitable chemical or mechanical pulping processcan be used in the invention. In some embodiments, the pulping step usesa chemical pulping process such as a kraft process, a sulfite process ora soda process. In the embodiment shown in FIG. 1, the process includesa kraft pulping process (the block labeled “digestion”) in which thelignocellulosic material is cooked with an alkaline cooking liquor toallow the wood chips to separate into pulp fibers without muchmechanical action. Any suitable effective alkali charge can be usedduring the kraft process, such as an effective alkali charge within arange of from about 10 to about 20.

The process including the pre-extraction step in combination with thepulping step may result in a pulp yield similar to that of pulpingalone. In addition, the recovery of the spent cooking liquor may bereduced compared to that of pulping alone. In one embodiment, thecooking time of the pulping step may be reduced compared to a processthat includes the same pulping step without the pre-extraction step.Further, in one embodiment, the effective alkali charge during thepulping step may be reduced compared to a process that includes the samepulping step without the pre-extraction step.

As shown in FIG. 1, the pulp may be washed following the pulping step(digestion). Any suitable pulp washing method can be used, such ascontacting the pulp with a wash water to remove impurities and remainingalkaline solution from the pulp.

One embodiment of the invention comprises the above-describedcombination of pulping step and pre-extraction step. Unlike the processdescribed in U.S. Pat. No. 4,436,586, this embodiment excludes the useof an acid hydrolysis step before the pulping step.

In other embodiments of the invention, the process further includes anadsorption step in which hemicellulose is adsorbed on the pulp. FIG. 1shows an adsorption step following the pulp washing step. In theillustrated embodiment, part of the aqueous solution containing theextracted hemicellulose from the pre-extraction step bypasses thepulping step and pulp washing and is combined with the pulp in theadsorption step. The term “adsorbed”, as used herein, includes anymechanism by which the hemicellulose is combined with the pulp, such asadsorption, absorption, impregnation, or the like. The hemicellulose canbe adsorbed on the pulp in any suitable manner. For example, the washedpulp can be contacted with the aqueous solution from the pre-extractionstep to adsorb a portion of the dissolved wood sugars includinghemicellulose onto the pulp fibers. Alternatively, the hemicelluloseadsorbed on the pulp in the adsorption step could be derived fromanother source.

In some embodiments of the invention, adsorption times are equal to orgreater than 5 minutes e.g. from about 5 to about 100 minutes, fromabout 10 to about 60 minutes, or from about 15 to about 30 minutes, andpulp consistency is from about 1% to about 15% e.g. from about 2% toabout 12% or from about 3% to about 10%. In some embodiments of thisinvention, adsorption pH is 7 or greater e.g. from about 7 to about 14,from about 9 to about 11 or from 10 to about 11 and adsorptiontemperature is within a range of from about room temperature to about150° C. e.g. from 50° C. to about 120° C. or from about 65° C. to about100° C. The adsorption of the hemicellulose and other sugars on the pulpincreases the pulp yield. In one embodiment, the pulp yield at the endof the adsorption step is higher than the pulp yield of a process thatincludes the same pulping step without the pre-extraction and adsorptionsteps. For example, the pulp yield may be increased by at least about1%, or by at least about 3%, on a dry material weight basis.

One embodiment of the invention comprises: providing a pulp from alignocellulosic material, and adsorbing hemicellulose on the pulp toincrease the yield of the pulp. The pulp and the hemicellulose may bederived from any source, such as from the above-described processes orfrom other sources. Also, other sugars in addition to hemicellulose maybe adsorbed. The adsorption step may be conducted at any time inrelation to any delignification and/or bleaching of the pulp (describedbelow); in some embodiments the adsorption is prior to delignificationand/or bleaching.

As shown in FIG. 1, the pulp at the end of the adsorption step may bereferred to as a brown stock pulp. Additionally, the process of theinvention may result in a sugar rich extract following the adsorptionstep, which is the aqueous solution including any hemicellulose andother sugars that are not adsorbed on the pulp during the adsorptionstep. This sugar rich extract is a feed stream which is available forthe production of value-added materials.

Optionally, the process can also include subjecting the brown stock pulpto delignification and/or bleaching to lighten the color of the pulp.For example, a lighter colored pulp is desirable for applications suchas paper making. The delignification and/or bleaching can be conductedat any time in relation to the adsorption step. Any suitable process(es)can be used, such as delignification and bleaching of the pulp withelemental chlorine, with oxygen, or with ozone.

In another embodiment of the invention, the pulp is subjected to adelignification process to remove lignin from the pulp, and the processresults in increased selectivity of the delignification process. Thefirst step of the process is providing a pulp from a lignocellulosicmaterial. The pulp can be provided from any suitable source. In oneembodiment, the pulp is provided by subjecting the lignocellulosicmaterial to a pulping process, and the process includes an additionalstep of pre-extracting hemicellulose from the lignocellulosic materialbefore the pulping process.

The next step of the process is adsorbing hemicellulose on the pulp. Thehemicellulose can be obtained from a pre-extraction process as describedabove or it can be obtained from a different source.

Lastly, the pulp is subjected to a delignification process to removelignin from the pulp. Any suitable delignification process can be used,such as any of those described above. In one embodiment, an oxygendelignification process is used.

Advantageously, the adsorbed hemicellulose increases the selectivity ofthe delignification process compared to the same process without theadsorbed hemicellulose. For example, the selectivity may be increased byat least about 10% or 20%. The selectivity can be defined in anysuitable manner. For example, the selectivity can be defined as ΔK/ΔV,where ΔK is the change in kappa number that measures delignification andΔV is the change in viscosity that characterizes carbohydratedepolymerization.

Trials Supporting the Invention

The following trials describe the conditions and results of the controlcooks (i.e. only alkaline cooking and washing, or extraction with purewater rather than an alkaline aqueous solution) and those supporting theinvention. In all cases mixed southern hardwood chips supplied byInternational Paper were used. Example 1 describes the control cookusing kraft pulping. It shows that the control kraft cook results in atotal yield of 46.57%, rejects of 0.072%, 16 kappa and 40.6 cPviscosity. Example 2 describes the results when the chips arepre-extracted with pure water, and then further treated as described inthe block diagram in FIG. 1. The pre-extraction time and temperature arevariables in this example. It shows that with pure water extraction, itis not possible to extract a significant amount of hemicelluloses fromthe wood without causing a sizable loss in yield (about 6-8%) for thefinal kraft pulp. In Examples 3-5 the extraction is performed withsolutions containing respectively NaOH, Na₂CO₃ and NaBO₂ (sodium metaborate) as alkali source to produce a near neutral extract. Then theextracted chips are further treated as described in the block diagram inFIG. 1. For all three alkali sources it is shown that the extractionprocess will not significantly affect the final kraft pulp yield andpulp viscosity compared to that of the control, while about 6-8% of thewood is dissolved in the extraction process.

The effect of cooking time and effective alkali charge during kraftcooking after extraction of the chips with Na₂CO₃, Na₂CO₃ plus 0.05% AQ(on wood), or NaBO₂ to produce a near-neutral extract is described inExample 6. The results in FIG. 2 show that at the same kappa number thetotal pulp yield after extraction with Na₂CO₃ followed by kraft cookingis about 1 and 0.5% lower than that of the control kraft cook at 15% EAcharge when using respectively 13 and 12% EA charge during cooking afterthe extraction. The results in FIG. 3 show that at the same kappa numberthe total pulp yield after extraction with NaBO₂ followed by kraftcooking at 12% EA charge is about 0 to 0.5% lower than that of thecontrol kraft cook at 15% EA charge. Finally FIG. 4 shows that at thesame kappa number the total pulp yield after extraction with Na₂CO₃ plus0.05% AQ followed by kraft cooking at 12% EA charge is about 1% higherthan that of the control kraft cook at 15% EA charge. Since theadsorption treatment may further increase the final pulp yield (on wood)by about 0.5 to 1%, this means that for the three extractions procedures(i.e. Na₂CO₃, Na₂CO₃ plus 0.05% AQ (on wood), or NaBO₂ to produce anear-neutral extract) following the scheme shown in FIG. 1 produces apulp with the same or higher total yield than that of the control kraftcook alone. Another important technical improvement of theseextraction/cooking schemes is that the EA during cooking can be reducedwith 3% to 12% compared to the control at 15% EA. This can alsoconfirmed by the results in FIG. 5 which shows that the kraft cooksperformed at 12% EA after extraction with Na₂CO₃ or Na₂CO₃ plus 0.05% AQproduce the same residual effective alkali (REA) content in the blackliquor at the same kappa number as that of the control kraft cook at 15%EA. This figure also shows that the REA in the black liquor afterextraction with NaBO₂ is approximately 1% lower than that of thecontrol. Finally FIG. 7 shows that the delignification rate is higherfor the kraft cooks performed at 12% EA after extraction with Na₂CO₃compared to the kraft control cook. This means that the time at thecooking temperature to obtain the desired kappa number may be reducedcompared to that of the control. The opposite is true for a kraft cookfollowing extraction by NaBO₂. The latter may be explained by the lowerREA in the black liquor, and thus it is required to increase the EAcharge during kraft cooking from 12 to 13% when it follows an extractionusing NaBO₂. However it should be pointed out that for each mole ofNaBO₂ there will also be two moles of NaOH produced if it is processedin the alkaline recovery process.

Example 1 Control Cooking Experiments

Kraft Pulping Conditions: Wood chips: Mixed southern hardwood. EffectiveAlkali: 15%. Sulfidity: 30% (on AA). Liquid to Wood Ratio: 4.5. CookingTemperature: 160° C. H-factor: 1500 hrs.

Results (average of 4 duplicate cooks): Screened Yield: 46.50%, Reject:0.072%; Total Yield: 46.57%. Kappa Number: 16.0. Viscosity: 40.6 (c.p.).

Comment: Carbohydrate analysis show that this wood mixture has arelatively high lignin content, and thus it was relatively hard to cookand resulted in a relatively low yield.

Example 2 Pure Water Pre-Extraction/Cooking/Washing/AdsorptionExperiments

Water Extraction Conditions: No chemicals were added. Liquid to WoodRatio: 4.5. Extraction Temperature: 100° C., 125° C., 130° C., 140° C.,150° C., 160° C. Extraction Time: 15 minutes; 45 minutes; 90 minutes.

Water Extraction Results: Pure water extraction leads to the removal ofabout 4˜12% of wood substance from Southern Mixed Hardwood chips, withthe removal increasing with extraction temperature at 90 minutesextraction time. The pH of the final extraction liquid decreases withincreasing extraction temperature from a pH of 4.4 at 130° C. to 3.56 at160° C. Sugar analysis shown that for pure water extraction the yieldloss after cooking is mostly due to xylan loss. GPC analysis shows thatthe degree of polymerization of the extracted sugars is relativelysmall. When the extraction temperature reaches or exceeds 140° C., thewood substance removal increases significantly.

Kraft Pulping Conditions: Effective Alkali: 12˜15%. Sulfidity: 30% (AA).Liquid to Wood Ratio: 4.5. Cooking Temperature: 160° C. H-factor: 1500hrs.

Kraft Pulping Results: Screened Yield: 38.55˜47.48% (with the yielddecreasing with increasing water extraction temperature). Reject:0.013˜0.29%. Total Yield: 38.71˜47.90%. Kappa Number: 16.0˜20.0(depending on EA level). Viscosity: 37.7˜98.0 (c.p.). About 2, 5.5 and8% lower pulp yield compared to control cook when the water extractiontemperature is 140, 150 and 160° C. respectively. The viscosities of thepulps obtained with water extraction are much higher than that of thecontrol.

Comment: With pure water extraction, it is not possible to extract asignificant amount of hemicelluloses without causing a sizable loss inyield for the final kraft pulp.

Adsorption Conditions: Temperature: 60˜90° C. Time: 30˜60 minute.Consistency: 4˜10%. The optimal adsorption conditions appear to be 60minutes at 60 to 90° C.

Adsorption Results: The pulp yield for at optimal adsorption conditionsis about 1˜2% higher than that of the control. The pulp yield gainincreases with the dissolved solid content of the extraction solution.

Example 3 NaOH Pre-Extraction/Cooking/Washing/Adsorption Experiments

NaOH Pre-Extraction Conditions: 3% NaOH (as Na₂O) was added. Liquid toWood Ratio: 4.5. Extraction Temperature: 130° C., 140° C., 150° C., 160°C. Extraction Time: 90 minutes.

NaOH Extraction Results: The extraction at 130 to 150° C. leads to theremoval of about 8% of wood substance from Southern Mixed Hardwoodchips. Residual solid content in the extraction liquor increasesslightly with increasing extraction temperature. pH value in theextraction liquid decreased with the increase of extraction temperaturebut remained close to neutral (8.2 to 6.1). The sugar analysis showsthat the yield loss after alkaline extraction and cooking is due both tocellulose and xylan loss. GPC analysis data shows that the molecularweight of the extracted wood sugars is larger than when extracting withpure water (higher DP).

Kraft Pulping Conditions: Effective Alkali: 12˜15%. Sulfidity: 30% (AA).Liquid to Wood Ratio: 4.5. Cooking Temperature: 160° C. H-factor: 1500hrs.

Kraft Pulping Results: Screened Yield: 44.92˜46.03% (depending on theextraction temperature). Reject: 0.01˜0.535%. Total Yield: 45.46˜45.95%.Kappa Number: 14.7˜20.7 (depending on EA level). Viscosity: 32.9˜52.7(c.p.). The final total pulp yield is only about 1% lower than thecontrol cook (46.5% without extraction). Use of 10% NaOH (on od wood) inthe water extraction also gives a significantly lower pulp yield,similar to that obtained with pure water extraction.

Adsorption Conditions: Temperature: 60˜90° C. Time: 30˜60 minutes.Consistency: 4˜10%. The optimal adsorption conditions appear to be 60minutes at 60 to 90° C.

Results: The pulp yield for this experiment is about 1˜2% higher thanthat of the control. The pulp yield improvement depends on the solidcontent in the adsorption liquid. Without controlling the pH, thetreatment also increases the kappa number by almost one unit, somelignin must be co-adsorbed.

Comment: When the extraction is performed with NaOH to produce a finalneutral solution, the extraction process will not significantly affectthe overall kraft pulp yield and pulp viscosity compared to that of thecontrol.

Example 4 Na2CO3 Pre-Extraction/Cooking/Washing Experiment

Na₂CO₃ Extraction Conditions: 3% Na₂CO₃ (as Na₂O) was added. Liquid toWood Ratio: 4.5. Extraction Temperature: 140° C. Extraction Time: 90minutes.

Na₂CO₃ Extraction Results: Extraction leads to the removal of about 8%of wood substance from a new supply of Southern Mixed Hardwood chips.The dissolved solids content in the extraction liquor decreases comparedto NaOH extraction in Example 3 at 140° C. (2.15 compared to 2.46%). ThepH of the extraction liquid is close to neutral. The sugar analysisshown that a relatively large amount of cellulose, lignin, andhemicellulose are extracted from the wood chips.

Kraft Pulping Conditions: Effective Alkali: 13˜15%. Sulfidity: 30% (AA).Liquid to Wood Ratio: 4.5. Cooking Temperature: 160° C. H-factor: 1500hrs.

Kraft Pulping Results: About 1% (at 13% EA) to 2% (at 15% EA) lowerkraft pulp yield compared to the control cook performed on the newsupply of Southern Mixed Hardwood chips. The pulp viscosity is similarto that of the control.

Comment: When the extraction is performed with Na₂CO₃, the pulp yieldand viscosity are similar to that of the control, while the EA charge inthe kraft process may be reduced compared to the control.

Example 5 NaBO2 Pre-Extraction/Cooking/Washing/Adsorption Experiments

NaBO₂ Extraction Conditions: 4˜5% NaBO₂ (as Na₂O) was added. Liquid toWood Ratio: 4.5. Extraction Temperature: 140° C. Extraction Time: 90minutes.

NaBO₂ Extraction Results: Adding only 4% NaBO₂ (as Na₂O, on od wood)leads to the removal of about 6% of wood substance from Southern MixedHardwood chips. pH value in the extraction liquid close to neutral. Thesugar analysis shows that a relatively small amount of glucan, mannanand lignin, but a relatively large amount of xylan was extracted fromthe wood chips. The NaBO₂ extraction preserves more cellulose in thewood than NaOH or Na₂CO₃ extraction.

Kraft Pulping Conditions: Effective Alkali: 13.5%. Sulfidity: 30% (AA).Liquid to Wood Ratio: 4.5. Cooking Temperature: 160° C. H-factor: 1500hrs.

Kraft Pulping Results: Screened Yield: 46.01% (depending on theextraction temperature). Reject: 0.045%. Total Yield: 46.06%. KappaNumber: 18.5. About 1% lower kraft pulp yield compared to control cook.

Adsorption Conditions: Temperature: 90° C. Time: 60 minutes.Consistency: 10%.

Adsorption Results: The pulp yield for this experiment is about 1%higher than that of the control. The kappa number changes afteradsorption depending on the final pH. A high pH does not increase thekappa number. If adsorption process is performed without controlling thepH, then the kappa number increases by almost one unit.

Comment: When performing the extraction with NaBO₂, the extractionprocess will not significantly affect the final kraft pulp yield andpulp viscosity compare to that of the control.

Example 6 Effect of Cooking Time and Effective Alkali Charge duringKraft Cooking after Extraction of the Chips with Na2CO3, Na2CO3 plus0.05% AQ (on Wood), or NaBO2 to Produce a Near-Neutral Extract

The kraft cooking conditions for the control without pre-extraction(called KP-x), after pre-extraction with 3% (as Na₂O on wood) of Na₂CO₃(called 3CX-x), after pre-extraction with 4% (as Na₂O on wood) of NaBO₂(called 4BX-x), and after pre-extraction with 3% (as Na₂O on wood) ofNa₂CO₃ plus 0.05% AQ (called 3CQ-xB) are shown below in Table 1.

TABLE 1 Extraction-Kraft Cooking Experiments for Southern MixedHardwoods Screen Time Total Yield Screened Yield Reject Kappa (minute)EA REA RUN (%) (%) (%) Number H-factor @160° C. (%) (g/L) KP-1 48.8248.75 0.06 18.8  1500 3:26 15 3.86 KP-2 48.46 48.42 0.04 17.5  1510 3:2615 2.69 KP-3 48.69 48.64 0.05 17.80 1560 4:00 15 — KP-4 48.01 47.93 0.0817.96 1210 3:00 15 2.91 KP-5 49.27 48.95 0.32 20.92  833 2:00 15 4.31KP-6 47.55 47.50 0.05 16.41 1650 3:40 15 2.76 KP-7 48.80 47.46 1.3421.44  689 1:40 15 4.53 3CX-1 44.70 44.64 0.06 12.55 1500 3:26 15 5.653CX-2 48.42 48.40 0.02 15.94 1380 3:26 13 2.98 3CX-3 46.43 46.40 0.0316.26  884 3:00 13 5.70 3CX-4 47.72 47.56 0.17 18.76  435 2:00 13 4.573CX-5 47.39 47.36 0.04 17.41  957 2:20 13 4.23 3CX-6 48.04 47.82 0.2220.92  689 1:40 13 5.34 3CX-7 46.96 46.83 0.13 15.71 1420 3:30 13 3.173CX-8 48.20 48.03 0.17 20.31  925 2:00 12 3.49 3CX-9 47.35 47.30 0.0516.87 1191 2:40 12 2.49 3CX-10 48.16 48.09 0.07 16.34 1392 3:10 12 2.393CX-11 46.98 46.93 0.05 16.99 1490 3:40 12 3.05 3CX-12 48.63 48.52 0.1119.48 1042 2:18 12 3.45 3CX-13 48.08 47.98 0.09 17.51 1633 3:40 12 2.274BX-1 48.73 48.41 0.32 21.66  825 2:00 12 2.91 4BX-2 48.39 47.95 0.4520.67  965 2:21 12 2.46 4BX-3 47.85 47.80 0.06 17.90 2044 5:00 12 1.264BX-4 48.56 48.56 0.10 18.27 1500 3:32 12 1.80 4BX-5 48.75 48.67 0.0819.80 1460 3:36 12 2.39 4BX-6 46.29 46.27 0.02 16.08 3010 6:30 12 0.853CQ-1B 48.58 48.36 0.21 16.32 1220 3:00 12 2.76 3CQ-2B 48.94 48.72 0.2118.14  720 1:41 12 3.35 3CQ-3B 49.47 49.36 0.11 19.82  943 2:18 12 3.673CQ-4B 49.60 49.51 0.09 18.43 1420 3:31 12 2.29

As in Examples 4 and 5, the extraction time and temperature in allpre-extractions in this example are 90 minutes and 140° C. respectively.The liquor-to-wood ratio in both the pre-extraction and the kraft cookare 4.5 L/kg od. wood. After pre-extraction the liquor is drained fromthe chips (about ⅔ of the total present), and 30% sulfidity white liquorplus fresh water is added to obtain a liquor-to-wood ratio of 4.5 L/kgat the required effective alkali charge. The cooking time for both thekraft control and pre-extraction cooks was varied from 100 minutes to240 minutes at the maximum cooking temperature of 160° C. Total pulpyields, screened yields, reject contents, kappa number, and residualeffective alkali concentration were measured from the pulp samplesobtained from each cook.

The total yield for all experiments are displayed in FIG. 2. The resultsshow that the total pulp yield versus kappa number relationship for theextraction/kraft cooks runs parallel to that of the kraft control cooksover the range of bleachable pulp kappa numbers. At the same kappanumber the total pulp yield after extraction with Na₂CO₃ followed bykraft cooking is about 1 and 0.5% lower than that of the control kraftcook at 15% EA charge when using respectively 13 and 12% EA chargeduring cooking after the extraction. The results in FIG. 3 show theeffect of effective alkali charge during the kraft cook on the totalyield for the Na₂CO₃ pre-extraction cooks as compared to that of thecontrol kraft cook at 15% EA charge. It clearly shows the increase inyield for these pre-extraction cooks when the EA charge is reduced from15 to 12%. FIG. 4 shows that at the same kappa number the total pulpyield after pre-extraction with 4% NaBO₂ followed by kraft cooking at12% EA charge is about 0 to 0.5% lower than that of the control kraftcook at 15% EA charge. Finally FIG. 5 shows that at the same kappanumber the total pulp yield after extraction with Na₂CO₃ plus 0.05% AQfollowed by kraft cooking at 12% EA charge is almost 1% higher than thatof the control kraft cook at 15% EA charge. The residual lignin contentof the pulps (in % based on od wood) was determined by multiplication ofthe kappa number by 0.148 times the total yield (as fraction). Thelinear semi-logarithmic plots in FIG. 2 of the lignin content (based onwood) versus cooking time indicate first order delignification kinetics,with the slope being the delignification rate constant. The results inFIG. 6 show that the delignification rate for the Na₂CO₃pre-extraction/kraft cooks is higher than that of control kraft cook,while that of the NaBO₂ pre-extraction/kraft cook is lower than that ofthe control kraft cook. The results of the Na₂CO₃ plus 0.05% AQpre-extraction/kraft cooks display too much scatter to make a conclusionregarding the relative delignification rate. The effect of the EA chargeduring the kraft cook of the Na₂CO₃ pre-extraction/kraft cooks is seenmore clearly in FIG. 7. It shows that at 12 and 13% EA charge during thekraft cook of the Na₂CO₃ pre-extraction/kraft cooks, the delignificationrate is respectively about 30 and 40% higher than that of the controlkraft cook. The slower delignification rate of the NaBO₂pre-extraction/kraft cook relative to the control is shown separately inFIG. 8. The effect of these delignification rates on the development ofthe Kappa number versus H-factor are shown in FIG. 9. It shows that theNa₂CO₃ pre-extraction/kraft cooks reach a certain Kappa in a shortertime at the cooking temperature. It shows that at the same H-factor thekappa numbers of the Na₂CO₃ extraction/kraft cooks at 13% effectivealkali charge are about 3-5 lower units lower than those of kraftcontrol cooks at 15% effective alkali charge. Alternatively, at the samekappa number the H-factor can be reduced by about a factor 2 for theNa₂CO₃ extraction/kraft cooks at 13% effective alkali charge compared tothe kraft control cooks at 15% effective alkali charge. The reduction inH-factor compared to the kraft control cook are very small for theNa₂CO₃ extraction/kraft cooks at 12% effective alkali charge.

The residual effective alkali concentration in the black liquor sampleswas determined following the IP method. FIG. 10 shows that the Na₂CO₃extraction/kraft cooks at 13% EA charge produce a black liquor ofapproximately 0.5% higher REA than that of the kraft controls with 15%EA charge at the same final kappa number, while there is very littledifference in REA between the control kraft cook and the Na₂CO₃extraction/kraft cook at 12% EA. This result indicates that the hardwoodchips pre-extracted with a charge of 3% Na₂CO₃ (as Na₂O) consume about3% less effective alkali during the subsequent kraft cook compared to acontrol kraft cook. The percentage of screen rejects versus kappa numberfor the Na₂CO₃ and NaBO₂ pre-extraction/kraft cooks is shown in FIG. 11.Compared to the control it can be seen that the pre-extraction cooksgive less rejects at the higher range of kappa numbers.

Experiments Relating to Improved Delignification Selectivity

1. Wood Extract Preparation

Black Spruce wood meal was produced in the Wiley mill. The fractionpassing through a 20 mesh screen and retained on a 40 mesh screen wasused for experimentation.

100 g (oven dry basis) of the wood meal sieve fraction was mixed with800 ml 10% NaOH and kept at 60° C. for 12 hours. Then the extract wasremoved from the wood meal by filtration. The wood solution contained1.51% NaOH (determined by titration) and 3.02 other solids (determinedby gravimetry)

2. Oxygen Delignification

All oxygen delignification experiments were performed in ahorizontally-placed stirred batch reactor of Parr filled with 30 grams(oven dry basis) kraft pulp at 10% consistency.

The pulp was a softwood kraft pulp obtained from International Paper atJay, ME with a kappa number of 28.0 and an intrinsic viscosity of 1172ml/gram. 0.2% MgSO₄ (on o.d. pulp) and variable charges of NaOH and woodextracts were added to the pulp and the mixture was added to the Parrreactor.

Oxygen delignification of the pulp was performed at 100 psig oxygenpressure at 90° C. for 60 minutes. In total three experiments wereperformed with the addition of the wood extract, while another fourtrials without addition of wood extract served as control experiments.The variable experimental conditions pulp and liquor analysis are shownin Table 2 below. In experiment 3 the pulp was first mixed with theextract, and after about an hour the extract was removed by washing (twotimes at 1% consistency). Then MgSO₄ and NaOH were added to the washedpulp for subsequent oxygen delignification.

TABLE 2 Results of Oxygen Delignification Experiments NaOH IntrinsicWashing addition Kappa viscosity Residual Extract after (% on O₂ O₂delig. Pulp alkalinity Experi- addition extract o.d. delig. Pulp Yield(g ment (grams) addition pulp) pulp (ml/g) (%) NaOH/L) 1  10 No 2.5 16.4947 97.2 1.48 2 100 No 0   14.3 930 98.9 3.04 3 100 Yes 2.5 15.7 95497.9 1.12 Control n.a. n.a. 2.5 16.1 937 97.6 1.56 1 Control n.a. n.a.2.5 15.9 928 97.5 1.60 2 Control n.a. n.a. 3.0 15.5 912 97.0 1.40 3Control n.a. n.a. 4.5 13.8 849 96.7 3.35 4

3. Evaluation of the Results

Because the extract contains alkali, the experiments should be comparedat the same final alkalinity of the liquor. Thus by comparison ofexperiment 1 with controls 1, 2 and 3 it can be seen that at a lowaddition of 10 ml of extract (or about 1.0% charge of extract solids onpulp) there is no significant improvement in viscosity at the same kappanumber. Comparison of experiment 2 with Control 4 (with similar residualalkalinity) shows a significant viscosity improvement (estimated at50-60 ml/g at the same final kappa) and a pulp yield improvement ofabout 2%. Comparison of experiment 3 with control experiments 1, 2 and 3showed that viscosity was still improved but not the yield.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been described in itspreferred embodiments. However, it must be understood that thisinvention may be practiced otherwise than as specifically describedwithout departing from its spirit or scope.

1.-23. (canceled)
 24. A process of treating a lignocellulosic materialcomprising: in a pre-extraction step, extracting hemicellulose from thelignocellulosic material, by contacting the lignocellulosic materialwith a solution of a basic material in water; then in a pulping step,separating the lignocellulosic material into pulp; then in an adsorptionstep, adsorbing the hemicellulose on the pulp; and then subjecting thepulp to a delignification process to remove lignin from the pulp. 25.The process of claim 24 wherein the adsorbed hemicellulose increases theselectivity of the delignification process at least about 10% comparedto the same process without the hemicellulose pre-extraction andadsorption steps.
 26. The process of claim 25 wherein the selectivity ofthe delignification process is increased at least about 20%.
 27. Theprocess of claim 25 wherein the pre-extraction step achieves theextraction of at least about 15% of the hemicellulose from thelignocellulosic material as measured on a dry material weight basis. 28.The process of claim 25 wherein the delignification process is an oxygendelignification process.
 29. The process of claim 25 wherein thelignocellulosic material is wood.
 30. The process of claim 24 whereinthe pulping step comprises cooking the lignocellulosic material in apulping liquor containing an alkali material to separate thelignocellulosic material into pulp, and wherein the effective alkalicharge during the cooking is 12% or 13%.
 31. The process of claim 30wherein the effective alkali charge during the cooking is 12%.
 32. Theprocess of claim 24 wherein the pulping step comprises cooking thelignocellulosic material in a pulping liquor containing an alkalimaterial to separate the lignocellulosic material into pulp, and whereinthe total pulp yield after the pre-extraction and pulping steps ishigher than the yield of the same process without the pre-extractionstep.
 33. The process of claim 32 wherein the basic material used in thepre-extraction step comprises alkali metal carbonate.
 34. The process ofclaim 32 wherein the basic material used in the pre-extraction stepcomprises alkali metal borate.
 35. The process of claim 32 wherein thetotal pulp yield is about 1% higher.
 36. The process of claim 32 whereinthe lignocellulosic material is wood.